This application claims the priority of German Patent Application No. 101 23 202.0 filed May 12, 2001, which is incorporated herein by reference.
The invention relates to a method for protecting a fluid-operated percussion device against no-load strokes, having a percussion piston that moves inside a work cylinder and impacts a tool, the piston having two piston surfaces of different sizes, of which the smaller surface, being active in the direction of the return stroke, is permanently connected to a pressure line that is subjected to the working pressure, while the larger piston surface, being active in the direction of the work stroke, is alternately connected via a control valve to the pressure line and a pressure-relieved return line; a control unit that includes a distributing regulator, which moves inside the control valve and has two regulator surfaces that differ in size and are active in opposite directions of movement, with the smaller of the surfaces, which acts on the distributing regulator in the direction of the return-stroke position of the regulator, being permanently connected to the pressure line, and the larger regulator surface being connected only alternately and temporarily to the pressure line and the return line via a circumferential groove disposed between the piston surfaces; a no-load-stroke port that opens into the interior of the work cylinder, with the port first being opened toward the interior by the front piston collar of the percussion piston with the smaller piston surface after the percussion piston has overshot the normal impact position by an established distance in the work-stroke direction until it has assumed a no-load-stroke position; and a safety element, which is disposed upstream of the no-load-stroke port, and can be switched between two end positionsxe2x80x94the inoperative position and the active positionxe2x80x94and is connected on the intake side to the pressure line and serves in exerting the working pressure that originates from the safety element onto the no-load-stroke port in the active position, or, in the inoperative position, serves in breaking the connection between the pressure line and the no-load-stroke port, in which instance the working pressure exerted on the no-load-stroke port in the active position blocks the distributing regulator in the work-stroke position by way of the circumferential groove, should the percussion piston attain the no-load-stroke position.
The invention further relates to an apparatus that is suited for executing the method.
Depending on the working and application conditions, it may be desirable to equip fluid-operated percussion devices with a mechanism that protects against no-load strokes, particularly in the interest of avoiding an undesired stress or resulting damage. The Japanese published, non-examined patent application Hei-10-80878 of Mar. 31, 1998, proposes a solution relating to a hydraulic percussion device.
German Patent Application 100 13 270.7 of Mar. 17, 2000, proposes to equip a fluid-operated percussion device of the generic type mentioned at the outset with a manually-operated no-load-stroke protection mechanism in the form of a switchable safety element such that the percussion piston is shut downxe2x80x94independently of other control-related circumstancesxe2x80x94should it reach a defined extended position in the direction of the work stroke.
It is the object of the invention to build upon the solution presented in the cited German patent application by providing a method and an apparatus that permit the no-load-stroke protection mechanism to be activated automatically, regardless of the manipulation of the device by an operator. The method and the apparatus are intended to be embodied such that the percussion device will not be shut down upon startup when it is subjected to the working pressure, but always can at least start up.
The object is accomplished according to a first aspect of the invention by a method of protecting a fluid-generated percussion devices of the type originally defined wherein the safety element is transferred from its inoperative position into its active position some time after the startup of the percussion device subjected to the working pressurexe2x80x94counter to the effect of a resetting mechanism that acts on the safety element. As a consequence of the operating mode of the percussion device, a larger activation force that counteracts the resetting action is generated continuously, or at least temporarily at recurring time intervals. This ensures that the safety element is always switched to be active due to the effect of the activation force after the percussion device has started up, in case the percussion piston moves in the work-stroke direction and may be able to reach the no-load-stroke position. As already mentioned, the subject of the invention can be embodied such that the safety element is either held continuously in the active position it has assumed once after the startup of the percussion device, or it is transferred again into its active position, at least in repeating intervals.
According to features of the invention, the method can be executed such that the safety element is transferred into its active position over the course of the first work cycle of the percussion piston or over the course of the first return-stroke movement of the percussion piston after the percussion device has started up. The work cycle encompasses the work-stroke and return-stroke movements, or the return-stroke and work-stroke movements, of the percussion piston. According to a teaching of the invention, the activation force acting on the safety element can be generated by the working pressure building up temporarily in a percussion-device line that is periodically subjected to pressure during the operation of the percussion device. Furthermore, the method can be embodied such that the safety element is temporarily transferred into its active position within the time frame, and maintained in this position while the percussion-device line is subjected to the working pressure.
The activation force acting on the safety element can be built up by the working pressure present in the no-load-stroke port. The safety element can, however, also be transferred into its active position if the larger piston surface of the percussion piston or the larger regulator surface of the distributing regulator is subjected to the working pressure for the first time after the percussion device has started up.
The method can also be embodied such that the safety element is gradually transferred into its active position, as a function of the operating period, after the percussion device has started up. For this to happen, a delay element can cause the safety element to execute a partial switching stroke per time unit in the direction of its active position, with the partial switching stroke being smaller than the switching stroke with which the safety element is transferred out of the inoperative position into the active position.
As an alternative, the control surface of the safety element can be supplied with a limited control volume, as a function of pressure fluctuations occurring periodically during the operation of the percussion device; consequently, the safety element is transferred in increments into the active position.
In a particularly simple embodiment of the subject of the invention, the limited control volume can be created by a percussion-device line equipped with a throttle element, which is periodically subjected to the working pressure during the operation of the percussion device. In this regard, the following lines in particular are considered as a percussion-device line: the alternating-pressure line, by way of which the larger piston surface of the percussion piston is temporarily exposed to the working pressure; the reversing line, by way of which the control valve of the percussion device can be switched into the work-stroke position; the short-stroke line, in the event that the percussion device is embodied to be switched between a long-stroke and a short-stroke mode; and the no-load-stroke line, whose mouth or port opens into the interior of the work cylinder.
In accordance with the invention, the limited control volume can also be created by a pump that conveys a constant volume for each work cycle during the operation of the percussion device. Also in this embodiment, the control surface, over which the safety element moves counter to the effect of the resetting mechanism, is only supplied with a limited control volume in numerous consecutive intervals. The control volume pushes the safety element in increments in the direction of its active position with each conveying action.
The above-mentioned conveying action can particularly be initiated when the pump is driven by a percussion-device line that is periodically subjected to the working pressure during the operation of the percussion device.
Within the scope of the invention, the aforementioned pump can also be replaced by other types of metering devices. In particular, it is possible to interpose a metering valve for acting on the control surface of the safety element, with the valve only briefly supplying a limited volume as a function of the change in certain pressure conditions that occurs repeatedly over time. As already mentioned, a percussion-device line that is periodically subjected to the working pressure can switch the metering valve between the blocking and flowing positions.
A suitable switching of the safety element can ensure that, after being transferred into the active position, the element is held in this position as long as the percussion device is being subjected to the working pressure.
The object of the invention is also accomplished according to a second aspect of the invention by an apparatus intended for executing the method that has the following features:
The safety element is an automatically-controlled two-position valve equipped with a resetting mechanism, and has a control surface that influences the mechanism""s position. This surface can be acted upon, by way of a signal line, by a pressure level that forms a control signal such that the two-position valve is transferred from its inoperative position to its active position some time after the percussion device has started up, and counter to the effect of the resetting mechanism. Moreover, the two-position valve is embodied such that it maintains its active position, attained with the control signal, at least in temporary, repeating intervals.
If the apparatus is configured such that the two-position valve only temporarily maintains its active positionxe2x80x94depending on the change in certain pressure conditions that occurs periodically in the operating mode of the percussion device xe2x80x94this naturally stipulates that the safety element must at least assume its active position during the work-stroke movement of the percussion piston, which can prevent no-load piston strokes anticipated to occur during this time. This is ensured in that the control valve is held securely in the work-stroke position by a corresponding exertion of pressure onto its relevant regulator surface; the control valve therefore can no longer be switched into its return-stroke position, and thus also cannot initiate the return-stroke movement of the percussion piston.
In a modification of the apparatus according to the invention, the signal line is connected to a percussion-device line, which is periodically subjected to the working pressure during the operation of the percussion device. The change in the pressure level occurring in repeating intervals in the relevant percussion-device line represents a signal that either causes the safety element to be transferred into its active position, or at least initiates the transfer.
The no-load-stroke line having the no-load-stroke port that opens into the interior of the work cylinder is particularly considered as a percussion-device line, as is the alternating-pressure line, by way of which the larger piston surface of the percussion piston is temporarily subjected to the working pressure, and the reversing line, by way of which the larger regulator surface of the distributing regulator that constitutes the control unit, is temporarily subjected to the working pressure.
If the percussion device has a pilot control that cooperates with the control unit, and a short-stroke line that is connected to the pilot control and the interior of the work cylinder, the signal line can also be connected to the short-stroke line within the scope of the inventive teaching.
A common feature of the above-mentioned embodiments of the apparatus is that a control signal that influences the safety element is triggered at different times after the percussion device has started up.
As an alternative to one of the above embodiments, the subject of the invention can also be configured such that the signal line itself is connected to the rear cylinder segmentxe2x80x94independently of the alternating-pressure linexe2x80x94by way of which the larger piston surface of the percussion piston is temporarily subjected to the working pressure.
In another type of embodiment of the apparatus, the signal line is connected to the interior of the work cylinder such that the line is subjected to the working pressure by way of the front cylinder segment in the event that the percussion pistonxe2x80x94seen in the direction of the return strokexe2x80x94assumes a position outside of its normal impact position. In this case, the change in pressure conditions in the work-cylinder interior that occurs during the work cycles of the percussion piston is utilized to influence the position of the safety element.
The opening or port for the signal line into the interior of the work cylinder can be disposed at the level of the no-load-stroke port, or when seen in the direction of the return stroke of the percussion piston, can also be disposed in front of the no-load-stroke port. A crucial point in this connection is that the mouth of the signal line into the work-cylinder interior must be blocked by the percussion piston no later than when the piston has reached the impact position.
Moreover, the mouth or opening of the signal line into the interior of the work cylinder should be disposed in front of the mouth oar opening of the reversing line into the work-cylinder interior, when seen in the return-stroke direction of the percussion pistonxe2x80x94but, in any event, at the level of this mouth.
If the percussion device can be switched between a long-stroke and a short-stroke mode, the mouth or opening of the signal line into the work-cylinder interior can be located in the region that is limited by the mouth of the short-stroke bore on one side and the mouth of the reversing line into the work-cylinder interior on the other side.
In principle, the apparatus can also be embodied such that the safety element is gradually transferred into its active position after the percussion device has started up (through the exertion of the working pressure). This can be effected particularly in that the section of the signal line that is connected so as to permit a flow to the control surface of the safety element is connected to the signal source that acts on it such that a limited control volume is at least intermittentlyxe2x80x94 or, alternatively, continuouslyxe2x80x94supplied to the control surface after the percussion device has started up. This control volume causes the control surface either to execute a partial switching stroke per time unit, or advance in increments in the direction of the active position.
In this regard, embodiments that include a percussion-device line or a signal line that is connected to the interior of the work cylinder can be embodied correspondingly, i.e., the segment of the signal line that is connected to the control surface so as to permit a flow has a throttle element that acts as a delay element.
Because the pressure level in the relevant percussion-device lines and in the interior of the work cylinder changes periodically, the control surface of the safety element only advances in stages or steps in the direction of the active position under the additional influence of the throttle element.
In an embodiment having a continuous supply of a limited control volume, the segment of the signal line that is connected to the control surface so as to permit a flow is connected to the pressure line with the interposing of a throttle element that acts as a delay element. With the effect of the throttle element, which can be embodied as a throttle or baffle, the control surface is continuously supplied with a limited control volume per time unit; consequently, the safety element reaches its active position after a certain length of time.
The apparatus according to the invention can also be modified such that the segment of the signal line that is connected to the control surface of the safety element so as to permit a flow is equipped with a spring-loaded check valve, which blocks the signal line in the direction of the percussion-device line, or in the direction of the interior of the work cylinder. In this way, an undesired change in the pressure level in the percussion-device line or in the interior of the work cylinder can be barred from influencing the control surface of the safety element and changing the position of the element in a disadvantageous manner.
An apparatus similar to the switching mechanism of the safety element can be attained through the connection of a pump to the segment of the signal line that is connected to the control surface so as to permit a flow. This pump is driven such that it conveys a constant volume to the control surface per work cycle during the operation of the percussion device, which volume transfers the safety element into its active position in increments.
For switching the safety element into its inoperative position without a significant delay after the percussion device has been shut off, it should be ensured that the pressure level acting on the control surface can be suitably reduced. This can be effected in that the segment of the signal line that is connected to the control surface so as to permit a flow is additionally connected to the pressure line via a discharge line equipped with a spring-loaded check valve; in this instance, the check valve blocks the pressure line in the direction of the signal line.
If, after the percussion device has been shut off, the pressure level in the pressure line drops, the control surface can expel fluid into the discharge line and into the pressure line under the effect of the resetting mechanism when the check valve is open. Provided that the pressure line is subjected to the working pressure, the check valve assumes its blocking position, so the discharge line has no effect in the direction of the control surface of the safety element. As an alternative, the segment of the signal line that is connected to the control surface so as to permit a flow can additionally be connected to a throttle line, which is maintained in a pressure-relieved state through its connection to a throttle element disposed inside it. The throttle line can be pressure-relieved by being connected to the return line of the percussion device that terminates into the tank. After the percussion device has been shut down, the resetting mechanism of the safety element also influences the volume enclosed in front of the control surface, as described above, which volume can be carried off externally through the throttle line.
In an especially simple embodiment of the apparatus, the safety element is configured as an automatically-controlled 2/2-way valve. As an alternative, the safety element can also be configured as an automatically-controlled 3/2-way valve whose intake side is only connected to the pressure line, and whose discharge side is connected to the no-load-stroke mouth and to the signal line, with only the control surface being connected to the signal line in the inoperative position, and with the no-load-stroke mouth and the signal line that is connected to the control surface being subjected to the working pressure in the active position.
In a further embodiment of the apparatus according to the invention, the safety element is configured as an automatically-controlled 4/2-way valve whose intake side is connected to the pressure line and the signal line, and whose discharge side is connected to the no-load-stroke mouth and to an extension of the signal line, the extension being connected to the control surface so as to permit a flow. Furthermore, the 4/2-way valve is configured such that, in the inoperative position, the connection between the pressure line and the no-load-stroke mouth is broken, while the signal line and its extension are connected to one another. Finally, in the active position, the no-load-stroke port and the extension are subjected to the working pressure by way of the pressure line, and the signal line is blocked in the direction of the 4/2-way valve.
In the last mentioned embodiment, the safety element maintains the active position it has assumed oncexe2x80x94through the appropriate effect on its control surface after switchingxe2x80x94because in this position, the working pressure present in the pressure line is simultaneously exerted onto the control surface.
The invention is described in detail below by way of a plurality of exemplary embodiments that are illustrated in the drawing.